Will 19v external battery charge 20v Laptop?

zionlion02

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Dec 19, 2013
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What's up community -

Seems to be plenty of questions on the reverse, but I can't find anything about an under voltaged external battery. Most seem to go to 19v as the highest output.

Have a Lenovo u310 ultrabook. The power adapter says it's rated at 20v.

So my question, is whether or not a 19v external battery would have enough juice, and/or if it could damage my laptop battery.

I assumed only OVER voltage would harm it. But don't want to assume with electronics...

Thanks guys!
 

djjag1

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Dec 16, 2013
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I don't know about specifics in terms of your laptop or whatever, but I do know a little about electrics.

If your laptop battery is @ 20v, and you plug in a 19v battery, your laptop battery will try to charge the lower voltage battery as electricity tries to create an equal charge everywhere in a circuit. If both batteries were the same size, in theory they would both end up 19.5v.
I suspect though a laptop will have some diodes or something to prevent this, but either way it wouldn't charge.

If your laptop battery died, and was reading eg 17v, then the 19v battery could charge it up a little. You would need to have some sort of regulator in there to limit the amount of current flowing to the battery though, A simple resistor would do the job, but without knowing specifics I couldn't say what size.

So it's a kind of yes and no....

Surely a better option would be a few spare batteries?
 

zionlion02

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Dec 19, 2013
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HI there, thanks for jumping in! No my adapter is fine. I'm trying to get an external battery pack for when traveling and not near a plug.

Most of the external batteries seem to be up to 19v. So i'm just curious if that will still work.

Thanks!

 

djjag1

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Dec 16, 2013
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I don't know about specifics in terms of your laptop or whatever, but I do know a little about electrics.

If your laptop battery is @ 20v, and you plug in a 19v battery, your laptop battery will try to charge the lower voltage battery as electricity tries to create an equal charge everywhere in a circuit. If both batteries were the same size, in theory they would both end up 19.5v.
I suspect though a laptop will have some diodes or something to prevent this, but either way it wouldn't charge.

If your laptop battery died, and was reading eg 17v, then the 19v battery could charge it up a little. You would need to have some sort of regulator in there to limit the amount of current flowing to the battery though, A simple resistor would do the job, but without knowing specifics I couldn't say what size.

So it's a kind of yes and no....

Surely a better option would be a few spare batteries?
 
I don't recommend to replace the adapter with a battery. The charging circuit who deliver the voltage to the motherboard is expecting 20 volts continuously. The voltage from the 19V battery will drop slowly, the charging circuit is not designed for that.
 
Hi, @djjag1, FYI the battery is not removable in the Lenovo U310, so a spare battery is not an option to travel with it. The battery have 11.1 volts, so it's not @20V, your deduction for charging the battery don't apply for a laptop. Like you said you don't know about specifics about laptop. Best regards.
 

djjag1

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Dec 16, 2013
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@Jarotech. Thanks for the info. You learn something new every day.

In that case, OP, why not hook a car charger up to an external 12v battery. The output from it will be regulated and stable as the charger is designed for that purpose.
 
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